What does the R at the end of 10BNCHR stand for? Dr Rantfff only lists the following:

Bulova had a pretty straight designation system:
a number representing the rounded down width in lignes,
first letter: distinguishes between calibres of same size used in parallel,
second letter: generation of a particular calibre,
further letters:
A: automatic
B: day/date
C: sweep second
D: date only
L: no second (often used for blind men watches)

Current theory is that the "R" was indeed intended to represent Rail/Railroad. There are a fair number of pointers to this being its designated nomenclature. Its lack of becoming official as such, however, is the basis of a few different theories, all with varying degrees of support.